Invest in a luggage scale. Depending on what you choose they cost around $10 but they can save you a lot of money as well as time. If your luggage is overweight the fee can be expensive.
When we went to Italy we had one check on bag, When we got to the airport we found out it was overweight. We had to go through the suitcase and move things around to different bags and into our carry on until we got the weight down. It was a bit crazy standing at the counter rearranging our bags. We now have a small scale so we can check before arriving at the airport.
The funny part of this story is that the bag was my husbands because my daughter and I both packed in a carry on for our 10 day trip.